Prevention of clogging in CVD apparatus

ABSTRACT

Plugging of the effluent line of an apparatus comprising CVD chamber is prevented or substantially reduced by injecting a hot gas into the effluent line during processing. In CVD tungsten processing, including preconditioning the reaction chamber, deposition, and cleaning, a hot gas, such as dried air or nitrogen, is injected into the effluent line downstream of the vacuum pump to maintain the temperature of the internal walls of the effluent line below that at which condensation of WOF 4  occurs. In another embodiment, periodic high bursts of a hot gas into the effluent line removes WO 3  deposits proximate the inlet of the downstream wet scrubber.

TECHNICAL FIELD

The present invention relates to an apparatus comprising a chemicalvapor deposition (CVD) chamber having an effluent line in communicationwith a scrubber, and to a method of reducing clogging in the effluentline and scrubber. The invention has particularly applicability to amethod of manufacturing a semiconductor device employing tungsten(W)-CVD.

BACKGROUND ART

Conventional methods for manufacturing semiconductor devices comprisenumerous processing steps, many of which involve the deposition of ametal by CVD and subsequently etching portions of the deposited metal toform a conductive pattern and/or interconnection. Typically, such CVD isconducted in an apparatus comprising a CVD chamber. A conventionalprocessing sequence comprises preconditioning the chamber by introducingthe metallic species to be deposited prior to actual deposition, CVD,and cleaning the chamber. During such processing, vapors arecontinuously removed from the CVD chamber by a vacuum pump through aneffluent line. The effluent vapors, which include reaction products, areusually environmentally harmful. Accordingly, conventional practicesalso comprise employing a scrubber, such as a dry or wet scrubber, incommunication with the effluent line for treatment of vapors removedfrom the chamber.

Severe clogging problems usually occur in such conventional CVD systems.One type of acute clogging problem occurs in the effluent line due tocondensation of vapors resulting in the deposition of particulatematerial. Another clogging problem occurs proximate the inlet of a wetscrubber in the moisture-rich area, usually just above the watertip-over insert. For example, W is typically deposited during variousphases of manufacturing a semiconductor device by CVD employing tungstenhexafluoride (WF₆). A conventional apparatus employed for CVD comprisesa CVD chamber in which preconditioning, CVD, and chamber cleaning areconducted. Chamber cleaning typically comprises removing tungsten aswell as any reaction products from the internal walls of the chamber,and is conventionally conducted utilizing a fluorinated species such asSF₆ /O₂, NF₃ /O₂, CF₄ /O₂, C₂ F₆ or NF₃. Vapors are removed from the CVDchamber by a vacuum pump through an effluent line in communication witha downstream wet scrubber. Clogging of the effluent line and clogging inproximity to the inlet of the wet scrubber have become serious problemswhich result in equipment downtime, product uniformity, and exposure totoxic wastes.

A conventional apparatus utilized in the manufacture of semiconductordevices for CVD is schematically illustrated in FIG. 1 and comprises aCVD chamber 10. Process generated vapors are removed from chamber 10 byvacuum pump 11 through effluent line 12. As shown by the path of arrows,the vapors removed from chamber 10 are passed via effluent line 12 toscrubber 14. When employing a dry scrubber, a filter 13 shown in FIG. 1,is conventionally employed to remove particulate material. Whenemploying a wet scrubber, the depicted filter 13 is omitted. Theeffluent from the scrubber is exhausted through vent 15. Severe cloggingusually occurs in effluent line 12, particularly at elbows, such as at90° elbow 16. In addition, clogging usually occurs near the inlet of awet scrubber in the moisture-rich area.

A conventional wet scrubber, i.e., Vector ES-Series Fume Scrubber 20marketed by ATMI ECOSYS Corp., of Santa Clara, Calif., is schematicallyillustrated in FIG. 2. The relevant portions of the depicted wetscrubber comprise water inlet 21, tip-over insert 22, lower O-ring sealof the throat 23, nitrogen ports 24, upper O-ring seal of the throat 25,lower band clamp 26, upper and lower spoolpiece O-rings 27 and upperband clamp 28. Clogging usually occurs approximate the tip-over insertas at 29.

When depositing W by CVD in a conventional apparatus comprising a CVDchamber, particulate deposition and consequential clogging of effluentline 12 (FIG. 1), such as at elbow 16, is usually due to condensation oftungsten hexafluoride WOF₄, believed to be a by-product generatedprimarily during the chamber cleaning phase of a typical W-CVD process.WOF₄ is a white crystalline solid with a melting point of 100° C. and aboiling point of 185° C. The vapor pressure of the solid is about 1 Torrat 56° C.; and about 20 Torr at 100° C. Due to its extremely low vaporpressure, WOF₄ condenses out as a solid as the temperature decreasesalong the effluent line. Thus, in practice, effluent line 12 has beenfound coated with white dry WOF₄ powder all the way from the pump outletport to the inlet of the wet scrubber, resulting in severe cloggingproblems, particularly at elbows. It has been observed that as much as95% of the particulate clogging problem is attributable to WOF₄ powder.

In a conventional wet scrubber just above the water tip-over pipe, thereis a moisture-rich area which creates a different clogging problem thanthat caused by condensation of WOF₄ along effluent line 12. In themoisture-rich area of the wet scrubber, clogging occurs due to WO₃solids. It is believed that such WO₃ solids result during chamberprecoating and deposition steps, when a significant amount of unreactedgaseous WF₆ is released into the effluent line. WF₆ hydrolyzes in thepresence of moisture to generate WO₃ solids which are deposited in themoisture-rich area of the wet scrubber. In addition, during chambercleaning, gaseous WOF₄ in the exhaust system is usually hydrolyzed toform WO₃ solids.

Prior attempts to address particulate clogging in an apparatuscomprising a W-CVD chamber involve wrapping a heating blanket orelectrical heating tape around the effluent line to maintain the exhauststream at an elevated temperature above the condensation temperature ofWOF₄. This approach has not proved particularly affective, and frequent,time consuming, exhaust line cleaning is still required.

A prior attempt to address WO₃ clogging in a wet scrubber of anapparatus comprising a W-CVD chamber involves spraying water to dissolvedeposited WO₃. This solution has also not been found particularlyeffective and is quite cumbersome.

Accordingly, there exists a need to prevent or substantially reduceclogging in an apparatus comprising a CVD chamber, particularlydeposited WOF₄ in the effluent line of an apparatus for W deposition byCVD. There also exists a need for a simplified, cost-effective manner toreduce and/or remove deposited particulate material in a wet scrubberdownstream of and in communication with the effluent line, particularlydeposited WO₃.

DISCLOSURE OF THE INVENTION

An object of the present invention is an apparatus comprising a CVDchamber, which apparatus is substantially free of clogging in thechamber effluent line and downstream scrubber.

Another object of the present invention is a method of preventing orsubstantially reducing clogging in the effluent line of a CVD apparatusdue to vapor condensation.

A further object of the present invention is a method of preventing orsubstantially reducing clogging in the effluent line of a W-CVDapparatus by preventing condensation of WOF₄.

Another object of the present invention is a method of preventing orsubstantially reducing clogging caused by WO₃ in a wet scrubberdownstream of and in communication with the effluent line of a W-CVDchamber.

Additional objects, advantages and other features of the invention willbe set forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from the practice of theinvention. The objects and advantages of the invention may be realizedand obtained as particularly pointed out in the appended claims.

According to the present invention, the foregoing and other objects areachieved in part by an apparatus comprising: a chemical vapor depositionchamber; a vacuum pump having an inlet port and an outlet port, with theinlet port in communication with the chemical vapor deposition chamber;an effluent line in communication with the outlet port of the vacuumpump; a hot gas inlet line into the effluent line in proximity to theoutlet port of the vacuum pump; a gas heater in communication with thehot gas inlet line; and a source of gas in communication with the gasheater.

Another aspect of the present invention is a method of reducing cloggingin an apparatus comprising a chemical vapor deposition chamber due tocondensation of vapors, which method comprises injecting a hot gas intothe apparatus to maintain the temperature of internal walls of theapparatus above the temperature at which condensation of the vaporsoccurs.

A further aspect of the present invention is a method of reducingclogging in an apparatus comprising a chemical vapor deposition chamberdue to condensation of vapors, wherein the apparatus comprises a vacuumpump having an inlet port in communication with the chemical vapordeposition chamber and an outlet port in communication with an effluentline, which method comprises injecting a hot gas into the effluent linedownstream of and in proximity to the outlet port of the vacuum pumpunder conditions sufficient to prevent condensation of the vapors on theinternal walls of the effluent line.

Another aspect of the present invention is a method of manufacturing asemiconductor device, which method comprises: depositing tungsten bychemical vapor deposition on a substrate in a chemical vapor depositionchamber; exhausting vapors from the chamber by a vacuum pump through aneffluent line; and injecting a hot gas into the effluent line tosubstantially reduce clogging in the effluent line due to thecondensation of WOF₄ by maintaining the internal walls of the effluentline at a temperature above that at which condensation of WOF₄ occurs.

A further object of the present invention is a method of reducingtungsten oxide clogging in the moisture-rich area of a wet scrubbersituated downstream of and in communication with a tungsten-chemicalvapor deposition chamber via an effluent line, which method comprisesperiodically injecting a hot gas into the effluent line at a rate ofabout 250 to about 350 slpm for about 5 to about 30 seconds.

Additional objects and advantages of the present invention will becomereadily apparent to those having ordinary skill in this art from whichthe following detailed description, wherein only certain embodiments ofthe invention is shown and described, simply by way of illustration ofthe best mode contemplated for carrying out the invention. As will berealized, the invention is capable of other and different embodiments,and its several details are capable of modifications in variousrespects, all without departing from the invention. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically depicts a conventional CVD system.

FIG. 2 schematically depicts a portion of a conventional wet scrubber.

FIG. 3 schematically depicts a CVD system in accordance with the presentinvention.

DESCRIPTION OF THE INVENTION

The present invention addresses and solves the effluent line cloggingproblem occurring during metal deposition phases of conventionalsemiconductor manufacturing methods, as in forming an interconnectionpattern. As shown in FIG. 1, particulate deposition and, hence, cloggingoccurs in effluent line 12, particularly at elbows, such as at 90° elbow16. Conventional approaches to this particular problem comprise theapplication of an external electrical heating tape. This attemptedsolution to the effluent line clogging problem has been less thansuccessful. It is believed that the length, configuration and heattransfer characteristics of conventional effluent lines render itdifficult to address the effluent line clogging problem with an externalelectrical tape.

In accordance with the present invention, effluent line clogging in anapparatus comprising a CVD chamber is prevented or, at least,substantially reduced by the strategic injection of a hot gas into theeffluent line downstream of and in proximity to the outlet port of thevacuum pump used to exhaust vapors from the chamber, such as vacuum pump11 (FIG. 3), as at location 34. Thus, in accordance with the presentinvention, an apparatus is provided comprising a CVD chamber and avacuum pump having an inlet port in communication with the chamber andan outlet port in communication with the an effluent line, as in aconventional CVD apparatus. However, the apparatus according to thepresent invention further comprises a gas inlet line into the effluentline in proximity to the outlet port of the vacuum pump, a gas heaterand a source of gas.

An apparatus according to the present invention is schematicallydepicted in FIG. 3, wherein elements similar to those in theconventional apparatus schematically depicted in FIG. 1 bear similarreference numerals. The apparatus of the present invention furthercomprises a hot gas inlet line 30 into effluent line 12 in proximity tothe outlet port of vacuum pump 11, as at location 34, and a gas heater31 in communication with hot gas inlet line 30. A source of gas 33 isprovided in communication with gas heater 31 through line 32 which mayoptionally include a control valve (not shown). The source of gas 33 isprovided with a gas which, when heated and injected into the effluentline, is capable of maintaining the internal walls of the effluent lineat a temperature sufficiently high to prevent condensation of thegaseous species causing the clogging problem, such as WOF₄. In anembodiment of the present invention, the gas source comprises a sourceof dried air, nitrogen or an inert gas, preferably dried air ornitrogen.

In practicing the present invention, a hot gas is injected at astrategic location, such as at location 34 (FIG. 3) downstream of and inproximity to the outlet port of vacuum pump 11, through hot gas inletline 30. The hot gas is injected into effluent line 12 under conditionssufficient to prevent or substantially reduce clogging by condensationof a condensable gaseous species within effluent line 12, particularlyat elbows, such as 90° elbow 16.

Severe effluent line clogging is attributable to the condensation of aby-product gaseous species. In accordance with the present invention, ahot gas is injected at a temperature and rate sufficient to maintain theinternal walls of the effluent line at a temperature above that at whichthe gaseous species condenses. As one having ordinary skill in the artwould recognize, in order to prevent condensation of a gaseous species,the partial pressure of the condensable species must be maintained belowthe vapor pressure of the condensable species. In addition, inaccordance with the present invention heat loss can be reduced byproviding insulation around the effluent line. This can be accomplishedby the application of a conventional insulation tape, such as a foamtape, or electrical heating tape.

The present invention effectively prevents or substantially reduceseffluent line clogging in various CVD systems employed for thedeposition of various metallic species. In one embodiment of the presentinvention, effluent line clogging in a W-CVD system is prevented orsubstantially reduced by injecting a hot gas, such as dried air,nitrogen or an inert gas, into the effluent line under conditions toprevent condensation of WOF₄.

With reference to FIG. 1, clogging in effluent line 12 of a W-CVDsystem, i.e., an apparatus comprising a W-CVD chamber, is believed to beattributable to condensed WOF₄ powder which is generated primarilyduring the cleaning phase. A conventional W-CVD procedure comprisespreconditioning chamber 10, W-CVD, cleaning the chamber with afluorinated species. It is believed that most of the WOF₄ depositionand, hence, clogging occurs during the cleaning phase. In accordancewith the present invention (FIG. 3), a hot gas is injected into effluentline 12 downstream of and in proximity to the vacuum pump, as atlocation 34, under conditions, such as temperature and rate ofinjection, sufficient to prevent condensation of WOF₄ on the insidewalls of the effluent line. In one aspect of the present invention, thehot gas is injected continuously during processing, particularly duringcleaning. However, it is preferred to continuously inject a hot gas evenwhile the apparatus is not utilized for processing, to continuoussuitable temperatures.

The hot gas can be any gas which is capable of maintaining the internalwalls of the effluent line below the condensation temperature of thecondensable gaseous species, such as WOF₄, and does not detrimentallyaffect the apparatus or processing. Dried air, nitrogen and inert gaseshave been found suitable. In a preferred embodiment of the presentinvention, the hot gas is dried air or nitrogen, most preferablynitrogen.

In applying the present invention to a W-CVD system, the hot gas isinjected at a temperature and rate sufficient to maintain the internalwalls of the effluent line below the temperature at which WOF₄condenses. Based upon thermodynamic considerations, it is believed thatthe internal walls of the effluent line should be maintained at atemperature of at least about 60° C. to about 80° C. in order to preventcondensation of WOF₆. Accordingly, for a particular apparatus, dependingupon the materials of the system and design configuration, one havingordinary skill in the art could easily determine an appropriatetemperature and injection rate of the hot gas to achieve the objectiveof preventing cooling in the effluent line to maintain the internalwalls of the effluent line at a temperature sufficient to preventcondensation and, hence, deposition of WOF₄. It has been found that thecondensation of WOF₄ can be effectively prevented or substantiallyreduced in an effluent line by injecting the hot gas at a temperature ofabout 20° C. to about 260° C., preferably 40° C. to about 90° C. It hasalso been found that the hot gas can be introduced at a rate of about 10to about 300 standard liter per minute (slpm), such as about 10 to about100 slpm, preferably about 10 to about 25 slpm.

The present invention also addresses and solves the problem of cloggingin a wet scrubber utilized downstream of an effluent line in aconventional CVD system, particularly a W-CVD system. In accordance withanother embodiment of the present invention, undesirable WO₃ depositionin the wet scrubber, particularly proximate the inlet of a wet scrubber,is removed in an efficient and simplified manner by periodicallyinjecting a hot gas into the effluent line, as at location 34 in FIG. 3,at a high burst rate. When employing a wet scrubber, filter 13 isomitted. In an aspect of this embodiment of the present invention, a hotgas, such as nitrogen, dried air or an inert gas, is injected into theeffluent line of a CVD system at a high burst rate, such as about 250 toabout 350 slpm, for a few seconds, such as 5 to 25 seconds,periodically. For example, it was found that a very short hot nitrogenflush of about 300 slpm for about 10 seconds, once or twice a week, caneasily remove any accumulated film of deposited WO₃ in the moisture-richarea of a wet scrubber. This simplified, efficient technique obviatesthe need for preventive maintenance which requires opening the wetscrubber with an attendant disadvantage in downtime.

The present invention can be practiced by modifying conventional CVDequipment to provide a hot gas inlet line, gas heater and gas source,for the injection of a hot gas to reduce clogging in a CVD system and/orreduced clogging in a wet scrubber. Thus, the present invention hasapplicability to conventional CVD apparatus, particularly a conventionalW-CVD apparatus, such as the Novellus Concept One-Tungsten CVDapparatus, marketed by Novellus Systems in San Jose, Calif., or thosecommercially marketed by Applied Materials of Santa Clara, Calif.

The scrubber employed in practicing the present invention can be any ofthose commercially available, such as the Vector ES-Series FumeScrubber. In carrying out the present invention, any conventional meansfor heating the gas introduced into the effluent line can be employed.For example, when employing nitrogen, an EXS11550-2 circulation heatermanufactured by Colortech, Inc., Glen Burnie, Md., can be employed.

Although, various aspects of the present invention have been describedwith respect to the deposition of tungsten, the present invention hasapplicability to any type of CVD systems wherein plugging is encounteredin an effluent line due to the condensation of a vapor species and/orplugging in a wet scrubber. In accordance with the present invention,plugging due to the condensation of a vapor species is prevented orsubstantially reduced by injecting a hot gas, such as dried air,nitrogen or an inert gas, into the effluent line under conditionssufficient to maintain the internal walls of the effluent line at atemperature sufficient to prevent condensation of the vaporous specieswhich causes plugging. In addition, periodic flushes at a high burstalso effects removal of clogging in a wet scrubber, particularly in themoisture-rich area due to WO₃.

The present invention enjoys applicability with respect to variousconventional CVD systems which can be easily modified in acost-effective manner by providing means for injecting a hot gas intothe effluent line. The present invention, therefore, provides a solutionto serious plugging problems, particularly plugging problems in theeffluent line of a CVD system, in a relatively simplified and expedientmanner, thereby avoiding costly delays due to downtime and preventivemaintenance, increasing product throughput and product uniformity, andreducing exposure to toxic wastes.

Only the preferred embodiment of the invention and but a few examples ofits versatility are shown and described in the present disclosure. It isto be understood that the invention is capable of use in various othercombinations and environments and is capable of changes or modificationswithin the scope of the inventive concept as expressed herein.

I claim:
 1. A method of reducing clogging in an effluent linecommunicating with a chemical vapor deposition chamber due tocondensation of vapors in the effluent line, which method comprisesinjecting a hot gas from externally of the chemical vapor depositionchamber directly into the effluent line to maintain the temperature ofinternal walls of the effluent line above the temperature at whichcondensation of the vapors occurs.
 2. The method according to claim 1,whereinthe apparatus comprises a vacuum pump having an inlet port incommunication with the chemical vapor deposition chamber and an outletport in communication with the effluent line; and the method comprisesinjecting the hot gas into the effluent line downstream of and inproximity to the outlet port of the vacuum pump.
 3. The method accordingto claim 2, wherein the apparatus further comprises a wet scrubber incommunication with the effluent line downstream of the hot gas inletinto the inlet line.
 4. The method according to claim 1, wherein the gasis dried air, nitrogen or an inert gas.
 5. The method according to claim1, wherein the gas is dried air or nitrogen.
 6. The method according toclaim 2, comprising:chemical vapor depositing tungsten on a substrate inthe chamber; and injecting the hot gas into the effluent line underconditions sufficient to prevent condensation of WOF₄ on the internalwalls of the effluent line.
 7. The method according to claim 6, furthercomprising: preconditioning the chamber, and cleaning the chamber. 8.The method according to claim 7, comprisingcleaning the chamber with afluorinated species; and injecting the hot gas into the effluent lineduring cleaning.
 9. The method according to claim 8, wherein thefluorinated species is SF₆ /O₂, NF₃ /O₂, CF₄ /O₂, C₂ F₆ or NF₃, and thehot gas is dried air or N₂.
 10. The method according to claim 7,comprising injecting the hot gas into the effluent line duringpreconditioning, chemical vapor deposition, and cleaning.
 11. The methodaccording to claim 6, comprising injecting the hot gas at a temperaturesufficient to maintain the internal walls of the effluent line at atemperature of at least about 60° C.-80° C.
 12. The method according toclaim 6, comprising injecting the hot gas is injected at a temperatureof about 20° C. to about 260° C.
 13. The method according to claim 12,wherein the temperature is about 40° C. to about 90° C.
 14. The methodaccording to claim 6, comprising injecting the hot gas at a rate ofabout 10 to about 300 slpm.
 15. The method according to claim 14,comprising injecting the hot gas at a rate of about 10 to about 100slpm.
 16. The method according to claim 15, comprising injecting the hotgas at a rate of about 10 to about 25 slpm.
 17. The method according toclaim 6, wherein the apparatus comprises a wet scrubber downstream andin communication with the effluent line, and the method furthercomprises periodically injecting hot dried air or hot nitrogen at a rateof about 250 to about 350 slpm for about 5 to about 30 seconds to removedeposited tungsten oxide proximate the inlet of the wet scrubber.
 18. Amethod of manufacturing a semiconductor device, which methodcomprises:depositing tungsten by chemical vapor deposition on asubstrate in a chemical vapor deposition chamber; exhausting vapors fromthe chamber by a vacuum pump through an effluent line; and injecting ahot gas from externally of the chemical vapor deposition chamberdirectly into the effluent line to substantially reduce clogging in theeffluent line due to the condensation of WOF₄ by maintaining theinternal walls of the effluent line at a temperature above that at whichcondensation of WOF₄ occurs.
 19. The method according to claim 18,further comprising: preconditioning the chamber, and cleaning thereaction chamber; and injecting the hot gas during preconditioning,depositing, and cleaning.
 20. The method according to claim 19,comprising cleaning the reaction chamber employing a fluorinatedspecies.
 21. The method according to claim 20, wherein the fluorinatedspecies is SF₆ /O₂, NF₃ /O₂, CF₄ /O₂, NF₃ or C₂ F₆.
 22. The methodaccording to claim 18, wherein the hot gas is air, nitrogen, or an inertgas.
 23. The method according to claim 18, wherein the hot gas is driedair or nitrogen.
 24. The method according to claim 18, comprisinginjecting the hot gas into the effluent line at a temperature sufficientto maintain the internal walls of the effluent line at a temperature ofat least about 60° C.-80° C.
 25. The method according to claim 18,wherein the hot gas is injected at a temperature of about 20° C. toabout 260° C.
 26. The method according to claim 25, wherein the hot gasis injected at a temperature of about 40° C. to about 90° C.
 27. Themethod according to claim 18, comprising injecting the hot gas at a rateof about 10 to about 300 slpm.
 28. The method according to claim 27,comprising injecting the hot gas at a temperature of about 10 to about100 slpm.
 29. The method according to claim 28, comprising injecting thehot gas at a temperature of about 10 to about 25 slpm.
 30. The methodaccording to claim 18, wherein: the apparatus further comprises a wetscrubber in communication with the effluent line downstream of the hotgas injection.
 31. The method according to claim 30, further comprisingperiodically introducing hot dried air or hot nitrogen into the effluentline at a rate of about 250 to about 300 slpm for about 5 to about 30seconds to remove deposited tungsten oxide proximate the inlet of thewet scrubber.
 32. A method of reducing tungsten oxide clogging in themoisture-rich area of a wet scrubber situated downstream of and incommunication with a tungsten-chemical vapor deposition chamber via aneffluent line, which method comprises periodically injecting a hot gasfrom externally of the tungsten-chemical vapor deposition chamberdirectly into the effluent line at a rate of about 250 to about 350 slpmfor about 5 to about 30 seconds.
 33. The method according to claim 32,comprising injecting hot dried air or nitrogen.
 34. The method accordingto claim 1, comprising injecting the hot gas during idle time when theapparatus is not employed for chemical vapor deposition processing. 35.The method according to claim 18, comprising injecting the hot gasduring idle time when the apparatus is not employed for chemical vapordeposition processing.
 36. The method according to claim 1, furthercomprising wrapping insulation around the effluent line.
 37. The methodaccording to claim 18, further comprising wrapping insulation around theeffluent line.
 38. The method according to claim 36, wherein theinjection of hot dried air or hot nitrogen substantially reducestungsten oxide clogging in a moisture-rich area of the wet scrubber. 39.The method according to claim 31, wherein the periodic introduction ofhot dried air or hot nitrogen substantially reduces tungsten oxideclogging in a moisture-rich area of the wet scrubber.
 40. The methodaccording to claim 31, comprising injecting the hot gas into theeffluent line during idle time when the apparatus is not employed forchemical vapor deposition processing.
 41. The method according to claim1, wherein the hot gas is injected externally to the chemical vapordeposition chamber.
 42. The method according to claim 18, wherein thehot gas is injected externally to the chemical vapor deposition chamber.43. The method according to claim 32, wherein the hot gas is injectedexternally to the chemical vapor deposition chamber.